The production of silverplated cutlery on an industrial level began in Germany in the middle of the 19th century. Two factors limited the output:
1. Access to electrical power was very limited at the time.
2. Electrical current was quite weak compared to the present day.

After some experimenting, engineers achieved the best results if they used a small bath, put one dozen table spoons and one dozen table forks in it, used 90 Grams of fine silver and then immersed the pieces until the silver anodes were dissolved and the silver had firmly settled on the cutlery. This took many hours and in the beginning made the finished pieces quite expensive. The engineers discovered that a little more than half of the 90 Grams used was spread on the 12 spoons (as they have a bigger surface than the forks), a little less than half was spread on the 12 forks. Using a larger bath would require a much longer plating process, which would have made the process even more expensive. To use more than the 12 + 12 pieces in a bath would result in:
1. The pieces closest to the silver anodes would get a much thicker plating.
2. The pieces farthest from the anodes would get a very thin plating.
So the thickness of the silver layer would differ considerably.

typical German 90 silverplate mark

Using 12 + 12 pieces as described above and 90 Grams of fine silver became a standard in Germany. To document this, the "90" was punched on the pieces. If companies wanted to produce cheaper cutlery, they used less silver, 60 Grams, 40 Grams or even 20 Grams, which made the plating very thin. Some used more, 100 or 150 Grams. Pieces were punched accordingly "60", "40", "20", "100" etc.

The plating process was adapted to other pieces of flatware and cutlery; knife-handles, smaller spoons, serving pieces etc., so that the silver layer on them was as thick as on the table spoons and table forks. As the same standard process was used, they all were stamped with the "90". New techniques made it possible to plate more pieces in bigger baths in shorter time, using much larger silver anodes. However, the thickness of the plating remained the same , so the marks remained the same.

WMF German 90 silverplate mark

When plated cutlery became more affordable and more and more customers bought it, they began to ask how much pure silver their flatware actually "contained". Manufacturers realized that they could use the answer as a method to promote sales and started punching a further mark that roughly provided the actual gram weight of the silver that coated the pieces. Unfortunately they used two different systems:
1. Pieces that usually come in a dozen (table- forks /-spoons / -knives, coffeespoons etc.) are punched with the weight of silver used for plating a dozen pieces. So tableforks and tablespoons were marked with a "45", smaller pieces were punched a lower figure (e.g. "35"), as less silver was needed to give them the same thickness of plating.
2. Pieces that usually came singly or in pairs (serving pieces) were punched with the weight of silver on a single piece.

Examples:
If you have a table spoon marked "90" and "45" it means: the standard process as described above was used, on one spoon roughly 1/12 of 45 Grams

(ca. 3,75 Grams) of fine silver were spread.
If you have a sugar tong marked "90" and "2" it means: again the standard process was used, 2 Grams of fine silver were used to coat the piece.
If you have a pair of salad servers, each piece marked "90" and "4" it means: again the standard process was used, on each piece 4 Grams of fine silver were used.

This German system of silverplate marking has been adopted by other European countries, and is sometimes seen on Dutch, Danish and Austrian silverplate.

  

FranceIn 1927, Gotthold Kehr wrote an (unpublished) doctoral thesis on the metalware industries of Saxonia, Germany. Having had access to the archives of major German manufacturers, his findings are considered reliable. Kehr notes, without naming his source, that it was Christofle of France, the most important maker of its time, that in the late 1860s, adopted the German production standards (as noted above) to French production - with the other French manufacturers following Christofle's lead.

Christofle "84" mark

Ercuis "10" mark, it indicates10 grams silver were used toplate the entire piece

Christofle made one notable change, instead of using 90 Grams of fine silver for electroplating, the company first used just 80 Grams, later upgraded to 84 Grams and the pieces were marked accordingly. Smaller pieces received the same thickness of silver plating as the larger pieces, but as less silver was used on them, they were marked accordingly "12 Gr.", "18 G." etc., basically the same as was done in Germany.

French silverplate pieces bear two marks:
1. The "84 Gr." (or "12 G." etc.) mark, most often in a square.
2. The maker's mark or retailer's mark, these never came in a lozenge (this form is found only on solid silver), but again most often in a square or rectangle. note; (both marks are sometimes combined, as in the illustrated Christofle example)

"84 g" and maker's mark as located on a French fork

The location of these two marks is typical of French flatware marking; not the handle reverse, but the front of the working ends; spoons are punched inside the bowl, forks just above the tines - the maker's mark to one side, the "84 G." mark to the other.

(cautionary note):

Russian "84" kokoshnik mark

Russian "84" kokoshnik

The "84" French silverplate mark is often mistaken for a Russian silver mark. There are notable differences between the marks on French plated pieces (as described above) and Russian silver marks. Though an "84" (but never with an additional "g" or "gr") may appear on Russian silver pieces (standing for a silver fineness of 875/1000), there is always more than one additional mark on Russian silver. In fact, there can or should also be: the maker's mark, a town mark, a warden's mark (sometimes with integrated date) and possibly a double-headed eagle as the mark of a court-supplier. All these marks are usually punched on the back of the handle, sometimes - not too often - on the back of the bowl of a spoon, but never - as the French do - on the inside of the bowl.